Flash memory is a type of electronic memory media that can hold its data in the absence of operating power. Flash memory can be programmed, erased, and reprogrammed during its useful life (which may be up to one million write cycles for typical flash memory devices). Flash memory is becoming increasingly popular as a reliable, compact, and inexpensive nonvolatile memory in a number of consumer, commercial, and other applications. As electronic devices get smaller and smaller, it becomes desirable to increase the amount of data that can be stored per unit area on an integrated circuit memory cell, such as a flash memory unit.
One conventional flash memory technology is based upon a memory cell that utilizes a charge trapping dielectric cell that is capable of storing two bits of data. One example of this type of non-volatile memory device is known as a dual-bit Flash electrically erasable and programmable read-only memory (EEPROM), which is available under the trademark MIRRORBIT™ from Spansion, Inc., Sunnyvale, Calif. Such dual-bit memory cells utilize a single silicon nitride layer having two separate charge storage regions to store charge within the silicon nitride layer. In such an arrangement, one bit can be stored using a first charge storing region on one side of the silicon nitride layer, while a second bit can be stored using a second charge storing region on the other side of the same silicon nitride layer. For example, a left bit and right bit can be stored in physically different areas of the silicon nitride layer, near left and right regions of each memory cell, respectively. In comparison to a conventional EEPROM cell, a dual-bit memory cell can store twice as much information in a memory array of equal size.